This invention relates generally to hydraulic systems, and more particularly to fuel injectors having hydraulically actuated control valves.
Several recent advances have been made in the area of hydraulically actuated fuel injectors. While many of these advances have been successful, engineers are always searching for ways to improve the performance of hydraulically actuated fuel injectors. For instance, in some hydraulically actuated fuel injectors, a pressure communication passage extends from a pilot valve to the top of the needle valve member, with a branch of this passage running to the underside of a spool valve to control movement of the same. One example of a fuel injector including such a configuration is described in U.S. Pat. No. 5,833,146, issued to Hefler on Nov. 10, 1998. While this design has performed well, a substantial amount of fluid flow past the pilot valve is required to move the spool valve due to the relatively large amount of fluid that must be displaced by movement of the spool valve member.
During cold start, when the oil in the pressure communication passage is relatively viscous, it is more difficult to displace the fluid past the relatively small flow area through the pilot valve to allow the spool valve to advance to its open position. This in turn can inhibit the fuel injector from performing optimally when the actuation fluid, typically oil, is viscous at cold start. In order to alleviate this need for substantial fluid flow around the pilot valve member, and to allow the fuel injector to perform closer to optimum at cold start, it would be desirable to make it easier to evacuate fluid from the underside of the spool, particularly during cold start and other high viscosity situations.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, a valve assembly includes a valve body that defines a first passage, a second passage and a variable pressure passage. A spool valve member is positioned in the valve body and is movable between a first position in which the first passage is open to the variable pressure passage and a second position in which the second passage is open to the variable pressure passage. A spool control volume is defined by at least one of the valve body and the spool valve member. A control valve member is positioned in the valve body and is movable between an open position in which the first passage is in fluid communication with the spool control volume and a closed position in which the first passage is blocked from fluid communication with the spool control volume. The control valve member includes a hydraulic surface that defines a hydraulic force direction. A biaser is operably in contact with the control valve member to produce a biasing force in opposition to the hydraulic force direction.
In another aspect of the present invention, a hydraulically actuated device includes a device body that defines a high pressure passage, a low pressure passage and a variable pressure passage. A source of high pressure actuation fluid is connected to the high pressure passage. A low pressure reservoir is connected to the low pressure passage. A spool valve member is movably positioned in the device body. A spool control volume is defined by at least one of the device body and the spool valve member. A control valve member is movably positioned in the device body and includes a hydraulic surface that defines a hydraulic force direction. The hydraulic surface is exposed to the high pressure passage when the control valve member is in a first position and is exposed to the low pressure passage when the control valve member is in a second position. The hydraulic surface is exposed to fluid pressure in a pressure cavity that is fluidly isolated from the spool control volume. A biaser is operably in contact with the control valve member to produce a biasing force in opposition to the hydraulic force direction. A reciprocating piston is included in the hydraulic device that has a hydraulic surface exposed to fluid pressure in the variable pressure passage.
In yet another aspect of the present invention, a method of operating a control valve includes providing a valve assembly that includes a valve body which defines a low pressure passage and a high pressure passage. A pilot valve member, a control valve member and a spool valve member are included in the valve body. The pilot valve member is moved from a first position to a second position to expose a hydraulic surface of the control valve member to the low pressure passage. The control valve member is then moved to a closed position blocking a control pressure surface of the spool valve member from the high pressure passage. Next, the spool valve member is moved from a first position to a second position. The pilot valve member is then returned to the first position to expose the hydraulic surface of the control valve member to the high pressure passage. The control valve member is next moved to an open position exposing the control pressure surface of the spool valve member to the high pressure passage. The spool valve member is then moved to the first position.